System and method for electrolytic plating

ABSTRACT

An electrolytic plating system for plating a via in a printed circuit board. The electrolytic plating system includes an electrolytic plating bath, a support rod supporting the printed circuit board in the bath, and means for alternately generating a laminar flow of electrolyte on each side of said printed circuit board.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Utility application Ser. No.10/273,820, filed Oct. 18, 2002, which is hereby incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

For the printed circuit boards of existing and future high technologyproducts, the problems of plating voids and poor plating distributionare becoming increasingly difficult due to the increase in aspect ratio.Printed circuit boards keep getting thicker and holes keep gettingsmaller. When a plating void is detected in a printed circuit board, theboard is rejected because of an open circuit.

Additionally, poor plating distribution can cause “dogbone” effects or,even worse, rejection of the board because of the fact that the minimumrequired thickness cannot be achieved inside of the (micro) via holes.

The present electrolytic plating invention seeks to overcome or minimizethese kinds of problems.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an electrolytic plating system in whichthe vibrator is mounted on a free, movable part of the flight bar. Thevibrator is not mounted on one of the massive (rigid) parts of the line.In prior art systems, a significant loss of vibration energy occursthrough absorption by the massive parts on which the vibrator ismounted. The mounting of the present invention allows all of the energyto be carried forward to the printed circuit boards in the plating line.Additionally, the energy transfer is more even compared to prior artsystems.

The manner in which the vibration energy is carried to the product ismore efficient and results in a dramatic reduction in plating voids.

The present invention also provides improved flow of the electrolytethrough the holes of the printed circuit boards, which generates animproved throwing power of plating inside of the through holes and blindvias. The improved flow is accomplished by an increase in laminar flowalong the printed circuit boards.

The laminar flow along the printed circuit boards is increased on oneside of the panel and generates an underpressure in the through hole.Because of this underpressure, electrolyte is drawn from the other sideof the panel through the hole to generate a better plating distribution.By bath movement, the laminar Row is moved from one side of the panel tothe other side. Accordingly, the underpressure is also moved from oneside to the other side and the eletrolyte is then drawn through the holein the opposite direction.

The increased flow is generated first by an eductor system that isplaced under specially designed floating shields. The resulting eductorsystem works like a venturi, so the volume of electrolyte that is pumpedthrough the eductor is increased 5 times when leaving the eductor.Second, the floating shield itself also creates a venturi flow becauseof it special design. The electrolyte exiting this floating shield hasmuch higher and better laminar flow as compared to standard platingdesigns.

BRIEF DESCRPTION OF THE: DRAWINGS

FIG. 1 illustrates the electrolytic plating apparatus;

FIGS. 2A and 2B illustrate partial end-views of the production line:

FIGS. 3A-B, 3C, and 3D-E illustrate the laminar flow patterns of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in FIG. 1, the electrolytic plating apparatus includes avibrator 11 attached to upper rod 13. The upper rod 13 is mounted with aspring system 12 to the rigid rod 14 that is used to support thev-saddles of the production line. The spring system 12 preventsvibration energy from being absorbed by the rigid parts of theapparatus.

The upper rod 13 carries the vibration energy from vibrator 11 andproduces homogeneous vibration energy to carry to lower rod 15. Clamps16, in which the printed circuit boards are fixed, are connected tolower rod 15, as is flexible current-supply connection 17.

As illustrated in FIGS. 1 and 2A-B, the system includes a specialfloating shield 20 in which the venturi flow effect is increased.Electrolyte is supplied through piping 21 to eductors 22 so as to drawadditional electrolyte from the bath.

As illustrated in FIGS. 2A-B and 3A-E, partitions 23 of floating shield20 are shaped to enhance the venturi effect 25 of the eductors 22.Partition 24 is located directly below the printed circuit boards andacts to direct the flow to either side of the boards, depending on thelocation of the shield 20. The partitions 23 also assist in producingthe improved laminar flow 26 along the printed circuit boards 31.

The laminar flow 26 causes the formation of a low pressure region (i.e.,Bernoulli effect) to draw an increased flow 33 of electrolyte throughthe through holes of the printed circuit boards 31, as illustrated inFIG. 2A. As shown in FIG. 2B, when the floating shield 20 is movedrelative to the eductors 22 by the transport movement, the laminar flowis directed to and increased on the opposite side of the printed circuitboard by partitions 23 and 24 so as to cause the flow 32 of electrolytein the opposite direction through the through hole.

FIGS. 3A-E show the transition of the laminar flow and through hole flowfrom the having the transport mechanism move the shield and itspartitions from the left (FIGS. 3A-B) of the eductors 22, to the middle(FIG. 3C). and then to the right (FIGS. 3D-E) of the eductors 22.

Although described with reference to a particular embodiment, one ofskill in the art would understand that various modifications can be madewithin the scope of the present invention. The present inventionincludes any electrolytic plating system with an electrolytic platingbath, means for positioning the printed circuit boards in the bath, andmeans to alternately generate a laminar flow of electrolyte on each sideof the printed circuit boards. A preferred means to alternately generatea laminar flow of electolyte comprises a floating shield with aventuri-shaped partition and an aligned partition below the printedcircuit boards, and plurality of eductors below the floating shield. Themeans to alternately generate a laminar flow of electolyte can furthercomprise a transport mechanism that moves the floating shield and itspartitions from side to side relative to the eductors or a mechanism tomove the eductors.

The plating can be further improved by using a vibrator and aspring-mounting system that prevents vibration energy being absorbed byfixed portions of the plating system.

An exemplary embodiment of the invention is an electrolytic platingsystem for plating vias and thru-holes in printed circuit boards thatincludes an electrolyte bath, a lower rod above the bath, a flexibleelectrical current supply connection attached to the lower rod, at leastone printed circuit board clamp attached to the lower rod, a floatingshield with v-saddles in contact with the printed circuit boards, thefloating shield further comprising a venturi-shaped partition, at leastone eductor in a lower portion of the bath below the floating shield forproducing a laminar flow of electrolyte across the printed circuitboards, and means to alternate the laminar flow from one side of theprinted circuit board to an other side of the printed circuit board.This system could also further comprise an upper rod that supports thelower rod, a vibrator on the upper rod, and a spring system to mount theupper rod to a rigid structure. The floating shield could furthercomprise a partition directly below the printed circuit boards to directflow of electrolyte to either side of the printed circuit boards and themeans to alternate the laminar flow can be provided by a transportmechanism that moves the shield and its partitions from side to siderelative to the eductors.

The invention can also be limited to the improvement in vibrationenergy, such as an electrolytic plating system for printed circuitboards comprising a plating line supporting the printed circuit boardswith a lower support rod, an upper rod that supports the lower rod, avibrator on the upper rod, and a spring system to mount the upper rod toa rigid structure.

Methods of practicing the present invention include an electrolyticplating method for plating vias and thru-holes in printed circuit boardsthat comprises positioning the printed circuit boards in an electrolyticbath and alternately generating a laminar flow of electrolyte on eachside of the printed circuit boards. Alternately generating a laminarflow of electrolyte can be provided by positioning a floating shieldwith a venturi-shaped partition and an aligned partition below theprinted circuit boards; and operating a plurality of eductors below thefloating shield, and can further comprise moving a transport mechanismso as to move the floating shield and its partitions from side to siderelative to the eductors. The method can further include supplyingvibration energy to the printed circuit boards in the bath by mounting avibrator on the transport mechanism using a spring-mounting system toprevent vibration energy being absorbed by fixed supports.

Another electrolytic plating method for plating vias and thru-holes inprinted circuit boards includes providing an electrolyte bath,positioning a lower rod above the bath, providing electrical current tothe lower rod with a flexible connection, clamping at least one printedcircuit board to the lower rod, transporting the printed circuit boardsin a floating shield with v-saddles in contact with the printed circuitboards, the floating shield further positioning a venturi-shapedpartition below the printed circuit boards. producing a laminar flow ofelectrolyte across the printed circuit boards with at least one eductorpositioned in a lower portion of the bath below the floating shield, andalternating the laminar flow from one side of the printed circuit boardto an other side of the printed circuit board. This method can furthercomprise supporting the lower rod with an upper rod, supplying vibrationenergy to the upper rod; and isolating the vibration energy from a fixedstructure with a spring system, as well as providing a partitiondirectly below the printed circuit boards to direct flow of electrolyteto either side of the printed circuit boards. Again, moving a transportmechanism that moves the shield and its partitions from side to siderelative to the eductors can be used to alternate the laminar flow.

Another electrolytic plating method for printed circuit boards of thepresent invention comprises supporting the printed circuit boards with alower support rod of a plating line, supporting the lower rod with anupper rod, supplying vibration energy to the upper rod, and mounting theupper rod to a rigid structure with a spring system.

It will be appreciated that various modifications and improvements maybe made to the described embodiments without departing from the scope ofthe invention, which is limited only by the claims, below.

1. An electrolytic plating system for plating a via in a printed circuitboard, comprising: an electrolytic plating bath; means for positioningsaid printed circuit board in said bath; and means for alternatelygenerating a laminar flow of electrolyte on each side of said printedcircuit board.
 2. The electrolytic plating system of claim 1, whereinsaid means for alternately generating a laminar flow of electrolytefurther comprises a floating shield with a venturi-shaped partition andan aligned partition below said printed circuit board and a plurality ofeductors below said floating shield.
 3. The electrolytic plating systemof claim 1, wherein said means for alternately generating a laminar flowof electrolyte further comprises a transport mechanism that moves thefloating shield and its partitions from side to side relative to saideductors.
 4. The electrolytic plating system of claim 1, wherein saidmeans for positioning said printed circuit board in said bath furthercomprises a vibrator and a system to prevent vibration energy beingabsorbed by fixed portions of said electrlytic plating system.
 5. Anelectrolytic plating system for plating a via in a printed circuitboard, comprising: an electrolyte bath; a support rod above said bath; aflexible electrical current supply connection attached to said supportrod; at least one printed circuit board clamp attached to said supportrod; a floating shield with v-saddles in contact with said printedcircuit board, said floating shield further comprising a venturi-shapedpartition; at least one eductor in a lower portion of said bath belowsaid floating shield for producing a laminar flow of electrolyte acrosssaid printed circuit board; and means for alternating said laminar flowfrom one side of said printed circuit board to an other side of saidprinted circuit board.
 6. The electrolytic plating system of claim 5,further comprising: an upper rod that supports said support rod; avibrator on said upper rod; and a spring system to mount said upper rodto a rigid structure.
 7. The electrolytic plating system of claim 5,wherein said floating shield further comprises a partition directlybelow said printed circuit boards to direct flow of electrolyte toeither side of said printed circuit boards.
 8. The electrolytic platingsystem of claim 7, wherein said means to alternate said laminar flowcomprises a transport mechanism that moves the shield and its partitionsfrom side to side relative to said eductors.
 9. An electrolytic platingsystem for printed circuit boards comprising: a plating line supportingsaid printed circuit boards with a lower support rod; an upper rod thatsupports said support rod; a vibrator on said upper rod; and a springsystem to mount said upper rod to a rigid structure.
 10. An electrolyticplating method for plating a via in a printed circuit board, comprising:positioning said printed circuit board in an electrolytic bath; andalternately generating a laminar flow of electrolyte on each side ofsaid printed circuit board.
 11. The electrolytic plating method of claim10, wherein the step of alternately generating a laminar flow ofelectrolyte further comprises: positioning a floating shield with aventuri-shaped partition and an aligned partition below said printedcircuit board; and operating a plurality of eductors below said floatingshield.
 12. The electrolytic plating method of claim 10, wherein thestep of alternately generating a laminar flow of electrolyte furthercomprises moving a transport mechanism so as to move the floating shieldand its partitions from side to side relative to said eductors.
 13. Theelectrolytic plating method of claim 12, further comprising the step ofsupplying vibration energy to said printed circuit board in said bath bymounting a vibrator on said transport mechanism using a system toprevent vibration energy being absorbed by fixed supports.
 14. Anelectrolytic plating method for plating a via in a printed circuitboard, comprising: providing an electrolyte bath; positioning a supportrod above said bath; providing electrical current to said support rod;clamping at least one printed circuit board to said support rod;transporting said printed circuit board in a floating shield withv-saddles in contact with said printed circuit board, said floatingshield further positioning a verituri-shaped partition below saidprinted circuit board; producing a laminar flow of electrolyte acrosssaid printed circuit board with at least one eductor positioned in alower portion of said bath below said floating shield; and alternatingsaid laminar flow from one side of said printed circuit board to anotherside of said printed circuit board.
 15. The electrolytic plating methodof claim 14, further comprising: supporting said support rod with anupper rod; supplying vibration energy to said upper rod; and isolatingsaid vibration energy from a fixed structure mounted to the upper rod.16. The electrolytic plating method of claim 14, further comprisingproviding a partition directly below said printed circuit board todirect flow of electrolyte to either side of said printed circuit board.17. The electrolytic plating method of claim 16, wherein moving atransport mechanism moves the shield and its partitions from side toside relative to said eductors to alternate said laminar flow.
 18. Anelectrolytic plating method for a printed circuit board comprising:supporting said printed circuit board with a support rod of a platingline; supporting said support rod with an upper rod; supplying vibrationenergy to said upper rod; and mounting said upper rod to a rigidstructure with a system for preventing vibrational energy from beingabsorbed by the rigid structure.